Comparative Anatomy - Frames

I haven't been able to get a lot of information on the frame used on the R51RS. Clearly it was based on the R51 frame. From photos, the frame an additional brace in front of the rear fender, under the seat. Unlike the brace that was used in R51/3 frames, the brace was centered. The R51/3 brace was off center in order to accommodate the battery. I have some pictures of a couple of frames I own; 1938/1939 frame and a 1954 frame.

First the R51 frame:

 Simple gusset around the steering head

The frame had no bracing in the "interior" volume. Looks to be very flexible, not in a good way.

There is a spot for the battery right in front of the rear fender, on the right side

The R51/3 frame:

 Brace on the across the down tubes, right below the steering head (a little hard to see) and a second one that is easy to see

 Brace from front to the seat post, just as with the post-55 /2 frames

 Brace from top to bottom. Note that the battery box on the '54 frame not only had a "floor" but also a "back". Prior to '54, the battery only had a floor.

Don't mind the bandages. 

I will add that I weighed the two frames, both powder coated. The '54 frame is 5 pounds heavier that the '39 frame. The price of stiffness.